vyos@vyos:~$ generate pki ca install test
Enter private key type: [rsa, dsa, ec] (Default: rsa) ec
...
You are not in configure mode, commands to install manually from configure mode:
set pki ca test certificate '...'
set pki ca test private key '...'

vyos@vyos:~$ conf
WARNING: You are currently configuring a live-ISO environment, changes will not persist until installed
[edit]
vyos@vyos# run generate pki ca install test
Enter private key type: [rsa, dsa, ec] (Default: rsa) ec
...
2 value(s) installed. Use "compare" to see the pending changes, and "commit" to apply.
[edit]
vyos@vyos# comp
+pki {
+    ca test {
+        certificate ...
+        private {
+            key ...
+        }
+    }
+}